Wind immune microphone
Disclosed is an acoustic device comprising an enclosed housing defining an inner volume and having a front and a back; an acoustic port penetrating the front of the enclosed housing; a first and second sense structure attached to the inside of the housing and defining a gap between the first and second sense structures; a front volume defined by the portion of the inner volume between the first sense structure and the front of the housing; a back volume defined by the portion of the inner volume between the second sense structure and the back of the housing; and at least one vent in the first sense structure operatively connecting the front volume and the gap, wherein the acoustic device has a cutoff frequency above approximately 100 Hz.
1. An acoustic device, comprising:
an enclosed housing defining an inner volume and having a front and a back;
an acoustic port penetrating the front of the housing;
a first and second sense structure attached to the inside of the housing and defining a gap between the first and second sense structures;
a front volume defined by the portion of the inner volume between the first sense structure and the front of the housing;
a back volume defined by the portion of the inner volume between the second sense structure and the back of the housing; and
at least one vent in the first sense structure operatively connecting the front volume and the gap, wherein the acoustic device has a cutoff frequency above approximately 100 Hz.
2. An acoustic device, comprising:
an enclosed housing defining an inner volume and having a front and a back;
an acoustic port penetrating the front of the housing;
a support structure attached to the inside of the housing;
a first sense structure attached to the support structure;
a second sense structure attached to the inside of the housing, the first and second sense structures defining a gap between the first and second sense structures;
a front volume defined by the portion of the inner volume between the first sense structure and the front of the housing;
a back volume defined by the portion of the inner volume between the second sense structure and the back of the housing; and
at least one vent in the support structure, the at least one vent operatively connecting the front volume and the gap, wherein the acoustic device has a cutoff frequency above approximately 100 Hz.
3. An acoustic device, comprising:
an enclosed housing defining an inner volume and having a front and a back;
an acoustic port penetrating the front of the housing;
a support structure attached to the inside of the housing;
a first and second sense structure attached to the support structure and defining a gap between the first and second sense structures;
a front volume defined by the portion of the inner volume between the first sense structure and the front of the housing;
a back volume defined by the portion of the inner volume between the second sense structure and the back of the housing; and
at least one vent in the support structure, the at least one vent operatively connecting the front and back volumes, wherein
the acoustic device has a cutoff frequency above approximately 100 Hz.
4. The acoustic device of claim 3 , further comprising:
a third sensing structure, the third sensing structure and the second sensing structure defining a second gap between the second and third sense structures, wherein the at least one vent operatively connects the front and back volumes.
5. An acoustic device, comprising:
an enclosed housing defining an inner volume and having a front and a back;
an acoustic port penetrating the front of the housing;
a first and second sense structure attached to the inside of the housing and defining a gap between the first and second sense structures;
a front volume defined by the portion of the inner volume between the first sense structure and the front of the housing;
a back volume defined by the portion of the inner volume between the second sense structure and the back of the housing; and
at least one vent in the second sense structure operatively connecting the back volume and the gap, wherein the acoustic device has a cut off frequency above approximately 100 Hz.
6. The acoustic device of claim 5 , further comprising:
a third sensing structure, the third sensing structure and the second sensing structure defining a second gap between the second and third sense structures, wherein the at least one vent operatively connects the first and second gaps.
7. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device is a condenser microphone.
8. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device is a MEMS device.
9. The acoustic device as in one of claims 1 - 4 , wherein at least one sense structure is flexible.
10. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device has a diaphragm compliance of approximately 1*10 −15 m 3 /Pa, a back volume less than approximately 5 mm 3 , and a vent resistance less than approximately 5*10 10 N-s/m 5 .
11. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device has a diaphragm compliance of approximately 1*10 −15 m 3 /Pa, a back volume less than 2 mm 3 , and a vent resistance less than approximately 1.1*10 11 N-s/m 5 .
12. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device has a diaphragm compliance of approximately 0.6*10 −15 m 3 /Pa, a back volume less than 2 mm 3 , and a vent resistance less than approximately 1.1*10 11 N-s/m 5 .
13. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device has a diaphragm compliance of approximately 0.6*10 −15 m 3 /Pa, a back volume less than 0.4 mm 3 , and a vent resistance less than approximately 5*10 11 N-s/m 5 .
14. The acoustic device as in one of claims 1 - 4 , wherein the acoustic device has a vent resistance, R 1 less than approximately (628*(C d +V/(142000)) −1 , where C d is the diaphragm compliance in m 3 /Pa, V is the back volume in m 3 , and R 1 is the vent resistance in N-s/m 5 .
15. The acoustic device as in one of claims 1 - 4 , wherein the gap includes only an air gap.
16. A method of forming an acoustic device, comprising the steps of:
forming an enclosed housing defining an inner volume and having a front and a back;
forming an acoustic port penetrating the front of the housing;
attaching a diaphragm having a compliance C d to the inside of the housing and separated a distance from the back of the housing, the diaphragm dividing the inner volume into a front volume and a back volume, the back volume having a compliance C v ;
forming at least one vent in the diaphragm, the vent having an acoustic resistance R 1 ; and
setting C d , C v and R 1 to non-zero values such that the acoustic device has a cutoff frequency f c of approximately 100 Hertz or greater, with f c defined by the equation
f
c
≈
1
2
π
R
l
(
C
d
+
C
v
)
.
17. A method of forming an acoustic device, comprising the steps of:
forming an enclosed housing defining an inner volume and having a front and a back;
forming an acoustic port penetrating the front of the housing;
attaching a support structure to the inside of the housing;
attaching a diaphragm having a compliance C d to the support structure and separated a distance from the back of the housing, the diaphragm dividing the inner volume into a front volume and a back volume, the back volume having a compliance C v ;
forming at least one vent connecting the front volume to the back volume, the vent having an acoustic resistance R 1 ; and
setting C d , C v and R 1 to non-zero values such that the acoustic device has a cutoff frequency f c of approximately 100 Hertz or greater, with f c defined by the equation
f
c
≈
1
2
π
R
l
(
C
d
+
C
v
)
.